This invention relates to the production of aluminum chloride in a molten salt bath and particularly to increasing the rate of formation of aluminum chloride.
Because of the continuing interest in producing aluminum by electrolysis of aluminum chloride there has been considerable effort expended in optimizing the formation of aluminum chloride in the process of reacting alumina containing materials with chlorine and with reducing agents such as carbon.
In the prior art, British Pat. No. 668,620 teaches the catalytic acceleration of the formation of aluminum chloride by alkali aluminum chloride. However, in that patent the reaction is carried out by contacting pulverulent alumina and alkali aluminum chloride with chlorine and carbon monoxide gases in a shaft furnace wherein the particulate solids are apparently suspended by the flow of the gases to prevent the particles from collapsing to form a dense mass.
In an article titled The Production of Anhydrous Chloride from .gamma.-Alumina in a Fluidized Bed, by Hille and Durrwachter, Angew. Chem. Internat. Edit. Vol. 72, 1960, pp. 73-79, it is suggested that iron, alkali metals and alkaline earth metals have a favorable effect on the aluminum chloride formation. That article concerns itself primarily with the formation of aluminum chloride in a fluidized bed which consists of alumina, gas and finely dispersed catalytically acting drops of molten sodium aluminum chloride. The article notes, however, that if the fluidized bed becomes fully loaded with sodium aluminum chloride melt, a rapid decrease in the reaction is experienced.
Such processes, while evidently producing aluminum chloride suitable for use as Friedel-Crafts catalyst or even for the electrolytic production of aluminum, tend to generate effluent dust containing many undesirable materials such as carbon, sodium aluminum chloride, carbon monoxide, phosgene, etc. which must be recaptured and separated to prevent the waste of chlorine values therein for economical reasons and to further prevent their escape to the atmosphere for ecological reasons.
The present invention provides for an improved process for the formation of aluminum chloride from alumina bearing materials, a chlorinating agent and a reducing agent in a molten salt bath by addition thereto of particular catalytic materials.